EP1464622A1 - Sauerstoffspeichermaterial enthaltend Cerium Oxide und mindestens ein anderes Metalloxid , Verfahren zu dessen Herstellung , und Verwendung desselben als Katalysator - Google Patents

Sauerstoffspeichermaterial enthaltend Cerium Oxide und mindestens ein anderes Metalloxid , Verfahren zu dessen Herstellung , und Verwendung desselben als Katalysator Download PDF

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Publication number
EP1464622A1
EP1464622A1 EP03005493A EP03005493A EP1464622A1 EP 1464622 A1 EP1464622 A1 EP 1464622A1 EP 03005493 A EP03005493 A EP 03005493A EP 03005493 A EP03005493 A EP 03005493A EP 1464622 A1 EP1464622 A1 EP 1464622A1
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Prior art keywords
oxide
metal
oxygen storage
storage material
material according
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English (en)
French (fr)
Inventor
Tassilo Dr. Bog
Lothar Dr. Mussmann
Dieter Dr. Lindner
Martin Dr. Votsmeier
Matthias Dr. Feger
Egbert Dr. Lox
Thomas Dr. Kreuzer
Mamoun Prof. Dr. Muhammed
Othon Adamopoulos
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Umicore AG and Co KG
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Umicore AG and Co KG
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Priority to US10/389,834 priority Critical patent/US20040186016A1/en
Priority to EP03005493A priority patent/EP1464622A1/de
Priority to JP2004076950A priority patent/JP2004337840A/ja
Publication of EP1464622A1 publication Critical patent/EP1464622A1/de
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0242—Coating followed by impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/10—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of rare earths
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F17/00—Compounds of rare earth metals
    • C01F17/30—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/60—Compounds characterised by their crystallite size
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/90—Other properties not specified above
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to an oxygen storage material (OSC) on the basis of cerium oxide, a process for producing the same and its application in a catalyst for exhaust gas aftertreatment.
  • the oxygen storage material of the present invention contains cerium oxide, at least one second metal oxide and, preferably, a further metal oxide.
  • the oxides have a very fine particle size, a high resistance against sintering and a high oxygen storage and release capacity.
  • the oxygen storage materials of the present invention can he employed as a catalyst or catalyst component for purifying exhaust gases of internal combustion engines, especially of stoichiometrically operated otto engines.
  • the catalyst according to the present invention shows excellent activity for purifying harmful pollutants like carbon monoxide, nitrogen oxides and hydrocarbons.
  • Automotive exhaust gases consist mainly of carbon monoxide (CO), hydrocarbons (HC) and various nitrogen oxides (NOx) as pollutants.
  • catalytic converters have been employed which have more or less catalytic activity for the simultaneous oxidation of CO and HC and reduction of NOx.
  • the conversion of the pollutants is performed preferably under stoichiometric conditions, which means that the oxidizing and reducing constituents of the exhaust gas are just balanced so that oxidation of CO and HC and reduction of NOx to harmless carbon dioxide, water and nitrogen can be performed simultaneously.
  • the oxygen content of the exhaust gas under stoichiometric condition is around 0,7 vol.-%.
  • the ⁇ -value is defined as the air/fuel ratio (A/F) of the exhaust gas normalized to stoichiometric conditions.
  • the air/fuel ratio for stoichiometric combustion of conventional gasoline and diesel fuels is approximately 14,7 which means that 14,7 kilogram of air are needed to bum 1 kilogram of fuel completely.
  • so-called three-way catalysts are widely used for exhaust gas aftertreatment.
  • Three-way catalysts comprise a heat resistant carrier formed of cordierite or metal, a high surface area catalyst support, e.g. ⁇ -alumina, and at least one precious metal element of the platinum group elements which is supported on the catalyst support.
  • a heat resistant carrier formed of cordierite or metal
  • a high surface area catalyst support e.g. ⁇ -alumina
  • at least one precious metal element of the platinum group elements which is supported on the catalyst support.
  • an oxygen storage material on the basis of cerium oxide is used.
  • Oxygen storage materials are able to store oxygen in oxidizing atmosphere or release oxygen under reducing conditions, respectively.
  • the storage and release of oxygen is associated with a change of the oxidation state of Ce 3+ to Ce 4+ and vice versa.
  • the amount of oxygen uptake or release as well as the adsorbing/desorbing kinetics under dynamic exhaust conditions are strongly dependent on the chemical composition, synthesis conditions and structural parameters of a given material.
  • oxygen storage materials show higher resistance against sintering and a significant higher oxygen storage capacity when they are highly dispersed on the specific surface area of a thermally stable support oxide with a high surface area such as alumina.
  • the prior art discloses (US 6,306,794) a composite oxide support and a process for its preparation based on alumina with at least one member of the group consisting of ceria, zirconia or ceria-zirconia. Additionally, the described composite oxide may contain barium or lanthanum.
  • a solution of salts of a plurality of elements including at least one of cerium and zirconium, and aluminum, which define the composite oxide is first mixed with an alkaline solution with the use of high speed mixing means to form a precursor of oxide composed of the plurality of elements.
  • the precipitate is first dried and then calcined in air at 650 °C for 1 hour.
  • a high rotating agitator is used.
  • alkaline hydroxides which cannot be completely removed from the product.
  • the prior art also discloses a composite oxide and a process for its preparation consisting of an oxide of a metal M 1 of the group of Ce, Zr, alkali earth or rare earth metals in an amount of at least 50% per weight based on the total weight of the composite oxide, and an oxide of a metal M 2 of the group of Al, Ti or Si, whereas the metal oxide M 2 is not soluble in the oxide of metal M 1 and both metals are dispersed at the nanometer level.
  • the oxides of the metals M 1 or M 2 additionally may contain a further oxide of a metal M 3 of the group of Zr, alkaline earth or rare earth metal.
  • the material is prepared by mixing suitable precursors of the metal oxides in the desired amount and precipitated by addition of an aqueous ammonia solution, dried and finally calcined.
  • the present invention provides a superior oxygen storage material obtained by forming a co-precipitate from cerium and of at least another metal M 1 and finally drying and calcining the co-precipitate to form mixed oxide particles from cerium and the another metal M 1 (Ce/M 1 mixed oxide particles).
  • a superior oxygen storage material obtained by forming a co-precipitate from cerium and of at least another metal M 1 and finally drying and calcining the co-precipitate to form mixed oxide particles from cerium and the another metal M 1 (Ce/M 1 mixed oxide particles).
  • the combined solutions of precursors from cerium and the other metals are vigorously mixed to avoid aggregation of the forming precipitated particles.
  • the precipitated compounds are decomposed and transformed into the desired oxides.
  • an oxygen storage material comprising cerium oxide and at least one second oxide of a metal M 1 selected from the group consisting of alkaline earth metal, rare earth metal, zirconium, zinc, cobalt, copper and manganese wherein cerium oxide and the second metal oxide form Ce/M 1 mixed oxide particles is provided.
  • This material shows an unprecedented high oxygen storage capacity and excellent dynamic properties with respect to oxygen storage and release compared to conventional materials.
  • the oxygen storage material of the first aspect of the invention can be further stabilized against thermal sintering by doping or coating with an additional oxide of a metal M 2 , e.g. alumina, or any other thermally stable metal oxide.
  • a metal M 2 e.g. alumina, or any other thermally stable metal oxide.
  • an oxygen storage material which comprises Ce/M 1 /M 2 mixed oxide particles and in a third aspect of the invention an oxygen storage material is provided, which comprises the Ce/M 1 mixed oxide particles of the first aspect of the invention coated with an oxide of the additional metal M 2 .
  • the additional metal M 2 is selected from the group consisting of aluminum, magnesium, zirconium, silicium, titanium, gallium, indium, lanthanum and mixtures thereof.
  • the oxygen storage capacity of the storage materials according to the invention is evaluated with the so-called Temperature Programmed Reduction with hydrogen (H 2 -TPR).
  • H 2 -TPR Temperature Programmed Reduction with hydrogen
  • a pre-oxidized sample is heated from room temperature to 1000 °C with a heating ramp of 10 °C/min under a hydrogen containing atmosphere (5 vol.-% H 2 , 95 vol.-% Argon or Nitrogen).
  • the hydrogen which is consumed by reaction with stored oxygen as a function of temperature, is used as an indication of the total oxygen storage capacity (OSC).
  • the ignition temperature T ign where the hydrogen uptake starts and the temperature window, calculated from the half width of the TPR curve, can also be used for the evaluation of oxygen storage materials.
  • the oxygen storage material of the present invention is based on mixed oxide particles of cerium and at least one second metal M 1 (Ce/M 1 particles in the following).
  • these mixed oxide particles form a single phase solid solution.
  • Solid solution is an art recognized term and includes a homogenous solid that can exist over a range of component chemicals which are homogeneously mixed with one another on an atomic scale. A single phase exists when the solid exhibits only one crystallographic structure.
  • the material additionally comprises an oxide of a further metal M 2 , which form an additional oxide component of the mixed oxide particles of the first aspect of the invention.
  • the particles of the Ce/M 1 mixed oxide are coated with the oxide of the further metal M 2 . This latter embodiment has been found to be particularly advantageous because it prevents the particles from sintering under high temperature load.
  • the metals M 1 are selected from the group consisting of alkaline earth metal, rare earth metal, zirconium, zinc, cobalt copper and manganese.
  • the alkaline earth metals are group 2 metals on the periodic table of elements.
  • the rare earth metals are elements 58 though 71 on the periodic table of elements.
  • the preferred metals M 1 for forming the Ce/M 1 mixed oxide particles are calcium, zirconium, magnesium, lanthanum, praseodymium, neodymium, yttrium, cobalt, zinc, copper, manganese or mixtures thereof.
  • the most preferred M 1 metals are calcium and zirconium.
  • the metal M 2 of which the oxide can be present as an additional component of the Ce/M 1 mixed oxide to form Ce/M 1 /M 2 mixed oxide particles is preferably selected from the group consisting of aluminum, silicium, titanium, gallium, indium and mixtures thereof.
  • metal M 2 may be selected from the group consisting of aluminum, magnesium, zirconium, silicium, titanium, gallium, indium, lanthanum and mixtures thereof.
  • the oxygen storage material of the present invention may be constructed from e.g. Ce/Zr-mixed oxide particles coated with zirconium oxide to improve stability against sintering.
  • the most preferred M 2 metal is aluminum.
  • the oxide of metal M 2 is admixed with an oxide of a rare earth metal, preferably with lanthanum oxide.
  • the Ce/M 1 mixed oxide particles contains more than about 50 but less than about 99 mol-% of cerium relative to the composition of the Ce/M 1 mixed oxide particles and the oxide of metal M 2 is present in an amount of about 1 to about 80 mol.-% relative to the total composition of the oxygen storage material.
  • Such a material exhibits an exceptional high oxygen storage capacity measured by hydrogen uptake of at least about 0,9 mmol hydrogen per gram oxygen storage material.
  • the temperature window of the H 2 -TPR curve is wider than 120 °C.
  • the process for preparing the oxygen storage material of this invention comprises the following steps:
  • Drying is done at elevated temperature between 50 and 180 °C for a period of 1 to 20 hours in air.
  • the precipitated compounds are calcined in air at 350 to 500 °C for 1 to 10 hours, preferably at 400 °C for 4 hours.
  • the precipitated compounds are decomposed and transformed into the desired oxides.
  • the resulting oxygen storage material is termed as the fresh material in the following.
  • the above process can be modified by adding a precursor of an oxide of a further metal M 2 to step a) to obtain an oxygen storage material according to the second aspect of the invention.
  • a precursor of an oxide of a further metal M 2 is added to the suspension and is deposited onto the precipitate by adding a second precipitation agent to obtain an oxygen storage material according to the third aspect of the invention.
  • Ammonium oxalate is used preferably as the first precipitation agent.
  • Barium hydroxide is used as second precipitation agent for depositing M 2 on the surface of the Ce/M 1 particles.
  • the oxygen storage material is prepared by a co-precipitation process in a specially designed synthesis reactor.
  • the synthesis reactor comprises a precipitation reactor (1) and a hydrolysis reactor (2).
  • the precipitation reactor is a tubular flow reactor for mixing a precursor solution of cerium and the additional metals with a precipitation agent and precipitating the metals in the form of small primary particles suspended in the liquid phase of the solution and the precipitation agent.
  • the precursor solution is introduced into the tubular flow reactor at (3) and the precipitation solution at (4).
  • the two combined solutions form a precipitation mixture. Precipitation immediately starts after contact between the two solutions. Precipitation is completed after approximately 1 second.
  • the residence time in the tubular flow reactor should not be smaller than 0,1 second - but on the other hand should not be extended over 5 to 10 seconds to prevent the formed primary particles from aggregating.
  • the quality and speed of mixing of the two components is essential for obtaining small precipitated particles. Therefore additional means are provided for improving mixing of the components. It was found that bubbling nitrogen gas into the tubular flow reactor just below the liquid surface of the precipitation mixture gives good results with respect to particle size.
  • nitrogen gas is introduced into the tubular flow reactor via gas feed (9). Instead of bubbling nitrogen into the precipitation mixture it is also possible to insert an ultrasonic transducer into the tubular flow reactor and enhance mixing of the two solutions by ultrasound. In general, it is advantageous to create a turbulent flow in the tubular flow reactor to increase mixing quality.
  • the precipitation mixture is introduced slowly from the tubular flow reactor into the hydrolysis reactor (2), where the precipitate is allowed to equilibrate for approximately one hour under intense mixing with mixer (7). It is important to note that the pH-value of the solution in the hydrolyzing reactor (2) should be held constant, because the equilibrium of the precipitation reaction is pH dependent. To achieve this, the pH-value is online monitored by a pH meter (8) and corrected by addition of basic or acidic solutions via feed (5). The resulting product is recovered by filtration, washed with deionized water and finally calcined for 4 hours in air at 400 °C to yield the freshly prepared oxygen storage material.
  • Feed (6) is provided for adding a precursor solution of at least one oxide of a further metal M 2 , preferably alumina, to allow precipitating the precursor of M 2 onto the already precipitated particles. This leads to coating of the primary particles with the precipitate of metal M 2 .
  • Figure 2 generally shows two procedures for preparing the oxygen storage material according to this invention.
  • Process (A) is a simultaneous precipitation process for preparation of the oxygen storage materials according to first and second aspects of the invention while process (B) is a sequential precipitation process for preparation of the oxygen storage material according to the third aspect of this invention.
  • an aqueous solution A containing suitable precursors (e.g. nitrates) of cerium oxide and an aqueous solution D of a suitable precipitating agent (e.g. ammonium oxalate) are mixed in the desired molar ratio in a suitable mixing reactor (e.g. the tubular flow reactor (5) of the precipitation reactor (1) in Figure 1).
  • a suitable mixing reactor e.g. the tubular flow reactor (5) of the precipitation reactor (1) in Figure 1
  • the precursor solutions are premixed in a separate mixer before they come into contact with the precipitating solution D.
  • the precipitation leads to the formation of small primary particles Ce/M 1 or Ce/M 1 /M 2 still containing the anions of the precipitation agent.
  • the precipitated particles are separated from the liquid phase by filtration and are then dried and calcined to yield the desired oxygen storage material which in this case is a homogeneous composite oxide. During calcination the primary particles form larger aggregates.
  • Procedure (B) in Figure 2 describes the sequential precipitation process to obtain an oxygen storage material according to the third aspect of this invention.
  • the first preparation step is the same as for the simultaneous precipitation process. Contrary to the simultaneous precipitation process the precipitated primary particles are not separated from the precipitation mixture but a third precursor solution C is added containing the precursor of the oxide of metal M 2 . This precursor is then precipitated onto the already formed primary particles of the first step by suitably adjusting the pH-value of the combined solutions.
  • Suitable precipitating agents D for the process according to this invention are any inorganic or organic chemicals, which react with precursor solution A to a poorly soluble precipitate.
  • hydroxides, carbonates, oxalates, tartrates, citrates of elements of group 1-3 of the periodic table or their corresponding free acids can be used.
  • ammonium salts were used.
  • polydentate organic ligands such as oxalic acid or citric acid or their salts can be applied, which are working as a molecular spacer for the metal ions in the mixed metal oxide and lead to a high elemental homogeneity.
  • the degree of homogeneity of the synthesized material can be determined by measuring the elemental distribution of the calcined product by electron dispersive spectroscopy (EDS) and is defined as the ratio of the s tandard d eviation (sd) for each dopant over the a verage v alue (av).
  • EDS electron dispersive spectroscopy
  • the homogeneity of Zr and Ce is the (sd/av) of the ratio Zr/(Ce + Zr) and Ce/(Ce + Zr), respectively.
  • the resulting materials contain more than about 50 and less than about 99 mol-% of ceria.
  • the balance is formed by the oxide of metal M 1 .
  • M 1 is either zirconium, calcium or mixtures thereof.
  • XRD measurements indicate the formation of a single phase solid solution with crystallite diameters below about 17 nm.
  • this material has a higher OSC compared to a commercial reference material with the same composition.
  • the hydrogen uptake is found to be typically higher than 0.9 mmol H 2 per gram.
  • T ign ignition temperature
  • the degree of inhomogeneity of the materials is generally below about 5%.
  • a precursor solution C of at least one oxide of a further metal M 2 may be added in an amount of about 1 to about 80 mol-% before (eqs. 3a and 3b) or after the precipitation process (eq. 4b).
  • the oxide of metal M 2 is homogeneously distributed in the Ce/M 1 mixed oxide particles, whereas in the latter form the oxide of metal M 2 is heterogeneously deposited on the outer surface of the Ce/M 1 mixed oxide particles.
  • Figure 2 shows the schematic build-up of these two processes.
  • Equations (3a) and (3b) describe the simultaneous precipitation process (sim) while equations (4a) to (4c) describe the sequential precipitation process (seq).
  • L signifies the ligand of a precursor
  • PA the precipitation agent
  • A the anion of the precipitation agent.
  • ⁇ T indicates treatment at elevated temperature during calcination.
  • one or more rare earth element oxides preferably lanthanum oxide, in an amount of about 1 to about 60 mol-% may be admixed with the oxide of metal M 2 by adding to the precursor of the oxide of metal M 2 a precursor of e.g. lanthanum oxide.
  • the metal oxide M 2 O x is deposited on the surface of the oxygen storage material in the form of a (mixed) hydroxide by addition of a suitable basic solution.
  • a suitable basic compound can be any base such as ammonia, alkaline or alkaline earth hydroxides or tetraalkylammonium hydroxides. It is preferred to use alkaline metal free precipitation agents. Alkaline metals cannot be removed from the oxygen storage material during the calcination process. They would later on damage the honeycomb carriers coated with catalytic coatings comprising the oxygen storage material. It is therefore most preferred to use ammonia, tetraalkylammonium hydroxides or barium hydroxide as the precipitation agent.
  • the freshly prepared oxygen storage materials were used to determine the specific surface area (S BET ), crystallite diameter and inhomogeneity. Then they were subjected to a TRP-measurement to determine the oxygen storage capacity, ignition temperature T ign and width of TPR-curve. The obtained data are listed in Table 1.
  • the oxygen storage material used as reference example R1 is a commercial Ce 0,63 /Zro 0,37 -mixed oxide calcined at 400 °C for 4 hours.
  • the resulting precipitate was allowed to reach equilibrium with the hydrolyzing solution during one hour of stirring after which the precipitate was filtered off, washed twice with an aqueous solution of 0.01 mol/1 oxalic acid, dried overnight in air at 120 °C and finally calcined in air for 4 hours at 400 °C.
  • Example E1 (Ce 0.9 Ca 0.1 O 2 )
  • Example R2 An aqueous solution of 1.0 mol/1 cerium (III) nitrate hexahydrate solution and 1.0 mol/1 calcium tetra-nitrate solution were used instead of solely cerium (III) nitrate as in reference example R2. The procedure of Example R2 was followed.
  • the final product contained 90 at-% of cerium and 10 at-% of calcium.
  • the characteristics of this powder are summarized in table 1.
  • Example E2 (Ce 0.63 Zr 0.37 O 2 )
  • the final product contained 63 at-% of cerium and 37 at-% of zirconium.
  • the characteristics of this powder are summarized in table 1.
  • Example E3 (Ce 0.8 Zr 0.2 O 2 )
  • Example E2 was repeated with different molar ratios between cerium and zirconium.
  • the final product contained 80 at-% of cerium and 20 at-% of zirconium.
  • the characteristics of this powder are summarized in table 1.
  • Example E4 (Ce 0.9 Ca 0.1 O 2 x 0.5 Al 2 O 3 , sim)
  • an oxygen storage material comprising cerium, calcium and aluminum was prepared according to the simultaneous precipitation procedure described above.
  • the resulting precipitate was allowed to reach equilibrium with the hydrolyzing solution during one hour of stirring after which the precipitate was filtered off, washed twice with an aqueous solution of 0.01 mol/1 oxalic acid, dried overnight in air at 120 °C and finally calcined in air for 4 hours at 400 °C.
  • the final product contained of 90 at-% of cerium and 10 at-% of calcium.
  • the amount of alumina was 50 mol-% calculated on the basis of the molecular weight of the Ce/Ca mixed oxide. The characteristics of that powder are summarized in table 1.
  • Example E5 (Ce 0.9 Ca 0.1 O 2 ⁇ 0.5 Al 2 O 3 , seq)
  • an oxygen storage material comprising cerium, calcium and aluminum was prepared according to the sequential precipitation procedure described above.
  • the final product contained 90 at-% of cerium and 10 at-% of calcium and 50 mol-% of alumina calculated on the basis of the weight of the Ce/Ca mixed oxide.
  • the characteristics of that powder are summarized in table 1.
  • Example E6 (Ce 0.8 Zr 0.2 O 2 x 0.2 Al 2 O 3 , seq)
  • Another oxygen storage material was prepared according to the sequential precipitation process by precipitating an aqueous solution of 1.0 mol/1 cerium (III) nitrate hexahydrate solution, 1.0 mol/1 zirconium nitrate with an aqueous solution of 0.3 mol/1 ammonium oxalate.
  • the suspension was further treated according to example E5.
  • the final product contained of 80 at-% of cerium, 20 at-% of zirconium and 20 mol-% of alumina calculated on the basis of the weight of the Ce/Zr mixed oxide.
  • the characteristics of that powder are summarized in table 1.
  • Example E7 (Ce 0.8 Zr 0.2 O 2 ⁇ 0.4 Al 2 O 3 , seq)
  • the final product contained 80 at-% of cerium and 20 at-% of zirconium and 40 mol-% of alumina calculated on the basis of the weight of the Ce/Zr mixed oxide.
  • the characteristics of that powder are summarized in table 1.
  • Example E8 (Ce 0.8 Zro 0.2 O 2 ⁇ 0.4 Al 2 O 3 ⁇ 0.03 La 2 O 3 , seq)
  • the final product contained of 80 at-% of cerium, 20 at-% of zirconium, 40 mol-% of alumina and 3 mol-% lanthana calculated on the basis of the weight of the Ce/Zr mixed oxide.
  • the characteristics of that powder are summarized in table 1.
  • Example E9 (Ce 0.8 Zr 0.2 O 2 ⁇ 0.4 Al 2 O 3 ⁇ 0.03 La 2 O 3 seq, Ba)
  • the alumina-lanthana mixed oxide was precipitated by addition of an aqueous solution of barium hydroxide.
  • the final product contained 80 at-% of cerium, 20 at-% of zirconium for the Ce/Zr mixed oxide, 40 mol-% of alumina, 3 at-% lanthana calculated on the basis of the weight of the Ce/Zr mixed oxide.
  • the characteristics of that powder are summarized in table 1.
  • Example E10 (Ce 0.7 Zr 0.2 Ca 0.1 O 2 ⁇ 0.2 Al 2 O 3 , seq)
  • the final product contained 70 at-% of cerium, 20 at-% of zirconium, 10 at-% of calcium and 20 mol-% of alumina calculated on the basis of the weight of the Ce/Zr mixed oxide.
  • the characteristics of that powder are summarized in table 1.
  • the positive effect of coating of the doped cerium oxide by a further metal oxide, M 2 O x , especially when the coating process is performed sequentially can also be seen from Figure 4 and 5.
  • the coating leads to a stabilization of the specific BET surface area, which prevents the primary particles from sintering at elevated temperatures. This can be illustrated by the lower crystallite sizes.
  • a much broader temperature window of the TPR profile is observed, which can be attributed to the highly porous surface of the coating, whereby the gaseous components have a good access to the active sites of the oxygen storage material.
  • the light-off temperature T 50 for a certain pollutant is the exhaust gas temperature at which the respective pollutant is converted by 50 %.
  • the light-off temperature may be different for different pollutants.
  • the so-called CO/NOx crossover conversion is determined by changing the lambda value of the exhaust gas from a value below 1 to a value above 1 or vice versa. At lambda values below 1 NOx conversion (reduction to nitrogen) is high while CO conversion (oxidation to carbon dioxide) is low. With increasing lambda value conversion of NOx drops and conversion of CO increases. The conversion at the point of intersection is the CO/NOx crossover conversion.
  • the CO/NOx crossover conversion is the highest conversion which can be achieved simultaneously for CO and NOx. The higher this crossover conversion the better is the dynamic behavior of the catalyst.
  • the catalysts were prepared by coating conventional honeycomb carriers made of cordierite 62 cm -2 /0,17 mm (400 cpsi/6.5 mil) with catalytically active coatings containing several types of ceria/zirconia based mixed oxides according to table 1 and tested with respect to catalytic activity.
  • the catalysts according to this invention were prepared by using the following raw materials: La/Al 2 O 3 ⁇ -alumina, stabilized with 3 wt.-% lanthanum, calculated as lanthanum oxide, specific surface area as delivered: 140 m 2 /g; mean particle size: d 50 ⁇ 15 ⁇ m; Oxygen storage materials see table 1 BaO Barium oxide, technical purity Pd(NO 3 ) 2 Palladium nitrate Rh(NO 3 ) 3 Rhodium nitrate Catalyst Carrier cordierite; 62 cm -2 / 0,17 mm (400 cpsi/6.5 mil); volume: 0,6181
  • La-stabilized ⁇ -Al 2 O 3 , oxygen storage material R1 and BaO in the weight ratio of 6:6:1 were mixed in deionized water to obtain a dispersion with a solid content of 45 wt.-%.
  • the suspension was milled to a mean particle size of 2 to 3 ⁇ m.
  • a ceramic honeycomb carrier was dipped into this suspension to give a homogeneous coating with the desired washcoat loading, dried in air for 1 h at 120 °C and finally calcined in air for 2 h at 500 °C. Subsequently, the catalytic coating was impregnated with a solution of palladium nitrate, dried once again and calcined.
  • the complete layer contained the following amount of washcoat components:
  • This catalyst will be denoted in the following as RC1. All other catalysts listed in table 3 and 4 are denoted as RC2 and C1 to C10. Instead of oxygen storage material R1 these catalysts contain the storage materials R2 and E1 to E10 with the same weight proportions as in catalyst RC1.
  • composition of the model exhaust gas is given in table 2 and the results of catalytic test are represented in table 3.
  • Composition of model exhaust gas Component Concentration Component Concentration CO 0,7 vol.-% NOx (NO) 0,2 vol.-% H 2 0,23 vol.-% CO 2 13 vol.-% O 2 0,65 vol.-% SO 2 20 ppm C 3 H 6 666 ppm H 2 O. 10 vol.-% C 3 H 8 333 ppm N 2 remaining Light-off temperatures (T 50 ) of tested catalysts.
  • the CO/NOx crossover conversions were determined.
  • the lambda-value was continuously raised from 0,99 to 1,01 at two different temperatures (400 °C and 450 °C) and with a space velocity of 225.000 h -1 .
  • the NOx-conversion drops from a high conversion rate to a low conversion rate while the conversion of CO behaves oppositely.
  • the conversion value at the crossover point is the CO/NOx crossover conversion.
  • the light-off temperatures of the described catalysts represented by the T 50 values are shown in Table 3.
  • the T 50 values correspond to the temperatures where 50 % of the pollutants are converted.
  • the light-off temperatures of the catalysts containing the oxygen storage materials of the present invention are considerably lower compared to the reference catalyst RC1, especially when alumina-coated materials were chosen.
  • the best results have been obtained with the catalyst C9.

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EP03005493A 2003-03-17 2003-03-17 Sauerstoffspeichermaterial enthaltend Cerium Oxide und mindestens ein anderes Metalloxid , Verfahren zu dessen Herstellung , und Verwendung desselben als Katalysator Withdrawn EP1464622A1 (de)

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EP1710009A1 (de) * 2005-03-30 2006-10-11 Kabushiki Kaisha Toyota Chuo Kenkyusho Dieselabgaskatalysator
US8748052B2 (en) 2006-02-07 2014-06-10 The University Court Of The University Of St. Andrews Reversible fuel cell
WO2007091050A1 (en) * 2006-02-07 2007-08-16 The University Court Of The University Of St Andrews Reversible fuel cell
GB2439208A (en) * 2006-06-14 2007-12-19 Victrex Mfg Ltd Polymeric Material
US8629232B2 (en) 2006-06-14 2014-01-14 Victrex Manufacturing Limited Polymeric materials
EP1920832A1 (de) 2006-11-08 2008-05-14 L'AIR LIQUIDE, Société Anonyme pour l'Etude et l'Exploitation des Procédés Georges Claude Trägerkatalysator und dessen Verwendung zur Herstellung von Synthesegas
EP1920830A1 (de) 2006-11-08 2008-05-14 L'AIR LIQUIDE, Société Anonyme pour l'Etude et l'Exploitation des Procédés Georges Claude Gruppe-VIII-Metall-und-Zeroxid/Zirkoniumoxid-Katalysatoren zur katalytischen Oxidation oder Reformierung von Kohlewasserstoffen
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WO2009155063A1 (en) * 2008-05-28 2009-12-23 Battelle Memorial Institute Composite catalyst materials and method for the selective reduction of nitrogen oxides
EP2324919B1 (de) 2008-09-10 2016-04-13 Cataler Corporation Abgasreinigungskatalysator
CN103619758A (zh) * 2011-06-17 2014-03-05 罗地亚运作公司 具有高还原性的基于铈的、锆的和另外的稀土金属的氧化物的组合物，其制备方法及其在催化剂领域的用途
FR2977581A1 (fr) * 2011-07-04 2013-01-11 Rhodia Operations Composition consistant en un oxyde mixte de cerium et de zirconium a reductibilite elevee, procede de preparation et utilisation dans le domaine de la catalyse
CN103635430A (zh) * 2011-07-04 2014-03-12 罗地亚运作公司 由氧化铈-氧化锆混合氧化物组成的具有增强的还原性的组合物，生产方法以及在催化领域的用途
CN103635429A (zh) * 2011-07-04 2014-03-12 罗地亚运作公司 由氧化锆-氧化铈混合氧化物组成的具有增强的还原性的组合物，生产方法以及在催化领域的用途
WO2013004533A1 (fr) * 2011-07-04 2013-01-10 Rhodia Operations Composition consistant en un oxyde mixte de cerium et de zirconium a reductibilite elevee, procede de preparation et utilisation dans le domaine de la catalyse
CN104519996A (zh) * 2012-08-10 2015-04-15 丰田自动车株式会社 废气净化用催化剂及其制造方法

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